#app3 #circular {
  border: 1px solid black;
  width: 100px;
  height: 100px;
  margin: 5vw;
  border-radius: 50%;
  background-color: coral;
}
#app3 #circular.change {
  animation: circular 1s linear infinite;
}
@keyframes circular {
  0% {
  }

  100% {
    background-color: blueviolet;
  }
}
